Roller presses include a stationary roller and a second moveable roller. The stationary and moveable rollers are spaced apart from each other to define a nip between the rollers. The rollers are rotated to comminute material that may pass through the nip. The second moveable roller may be moveable away from the first roller to widen the nip and may be moveable closer to the roller to narrow the nip. Examples of roller presses may be appreciated from U.S. Pat. Nos. 880,035, 4,484,879, 4,838,156, 4,905,910, 5,192,030, 5,211,108 5,354,002, 5,405,091, 5,454,520, 5,505,389, 5,601,242, and 5,918,823 and U.S. Patent Application Publication Nos. 2009/0314868 and 2009/0236455.
A hydraulic cylinder may be attached to the moveable roller to move the roller for widening and narrowing the nip. The cylinder may also be configured to help maintain a width of the nip for the comminution of material when the rollers are comminuting crushable material. A fluid such as oil may be used to adjust the position of a piston of the hydraulic cylinder for moving the second roller. The fluid of the hydraulic cylinder may have a pressure set point that affects the positioning of the second roller when a roller press is moving to comminute material.
Roller presses are often configured so that the moveable roller moves to widen the nip when an uncrushable element passes through the nip. Such movement is often in response to the large pressure created by the rollers attempting to comminute the uncrushable element. Often, a relief valve is required to be opened to relieve the build up of pressure that occurs within the hydraulic cylinder that may result form such an occurrence. When the relief valve is opened, fluid may pass from the hydraulic cylinder to a storage tank to reduce the pressure within the hydraulic cylinder and other components of the roller press.
The relief valves often have to be relatively large for effectively reducing the build-up of pressure that may result from the presence of an uncrushable element passing through the nip. Such large relief valves are generally expensive and add a significant amount of cost to roller presses.
Moreover, there is typically a delay between when an uncrushable element passes through the nip and when the relief valve is opened to release the increased pressure that is created as a result of the presence of the uncrushable element. The components of the roller press experience the substantial increased pressure during this delay, which may increase the wear experienced by components of the roller press, reduce the life of the components of the roller press, and increase the time and expense required to maintain the roller press.
A new roller press is needed that may permit an elimination or significant reduction in the pressure experienced by components of the roller press while waiting for a relief valve to open to relieve a pressure increase that may result when an uncrushable element passes through the nip of a roller press. Preferably, such a roller press is configured to permit use of a relatively small relief valve, which may help reduce the cost of manufacturing such a roller press. The new roller press preferably includes design features that may also be utilized in other devices configured to comminute material such as vertical mills or roller mills.